Within the art there exists numerous caster designs. Some of the designs for casters provide for the swiveling of a wheel attached to the frame of, for example, a cart or the like. Typically, the caster includes at least one race within which ball bearings are provided. With these types of casters, the ball bearing must both support the load from the frame and allow for the swiveling of the wheel in relation to the frame. Depending on the design of the caster, there may be a great deal of wear on the ball bearings affecting the life of the caster. Inventors therefore have been working to improve the life of the casters by providing various designs to better distribute the load evenly on the ball bearing circumference. An example of such a patent is U.S. Pat. No. 4,316,305 which offsets the loading axis of the ball bearing to improve caster life. However, such a caster still attempts to provide both the load-carrying ability and the swiveling ability of the caster via one set of ball bearings. The portions making up the caster include mating parts cast or formed by some alternative metal working process. U.S. Pat. No. 4,316,305 teaches an improved caster assembly utilized in an inverted disposition for its components. The fundamental improvement with this particular patent is the offsetting of the loading through the bearing elements 28.
Also within the art, there are various structures which attempt to separate the load carrying bearings and the swivel bearings by providing a double-ball caster with one set of bearings providing the load carrying ability, and the other set of bearings providing the swivel capability.
An example of such a structure is found in U.S. Pat. No. 4,777,697. Within the teachings of this patent, an outer load-carrying bearing set 3 is provided and an inner swivel or pivot-bearing set 4 is provided. A pin 8, or a king pin as it is known in the trade, secures the two portions together as is best seen in FIG. 3. One of the drawbacks of the design is the actual provision of the pin itself. Such pins normally will not fair well for casters supporting heavy loads. Typically, for such capacities of up to 30 tons, a bolt of very, very large diameter would have to be provided which would render the design economically unfeasible.
U.S. Pat. No. 3,127,633 is another example of a design including a king pin. The design incorporates hardened steel bearings operating in hardened races. The yoke is stamped or pressed from suitable sheet material such as low carbon sheet steel. An upper race portion 62 and a lower race portion 66 are therefore provided. U.S. Pat. No. 5,461,753 also describes a double-ball caster including a king pin 28 therewith.
U.S. Pat. No. 1,838,678 teaches a heavy-duty caster including auxiliary side thrust bearings provided within recesses having a general FIG. 8 configuration. The unit is fairly compact in design which is held together with a nut 46. This unit therefore will be successfully loaded up to the maximum load-carrying ability of the threaded fasteners.
Another example of a heavy duty caster assembly is found in German Patent Application No. DE 3,239,298 which teaches as best as can be determined a mass-produced assembly also including a double-ball arrangement including a pin for interconnecting the portions together.
Some designs for casters having a double-ball configuration have attempted to eliminate the need for a king pin altogether. U.S. Pat. No. 4,620,342 and European Patent No. 440,068 deal with similar structures in relation to a double-ball caster wherein the outer race is welded to a first portion of the fork, and the inner race is welded to the trolley. Both patents describe structures which do not incorporate a king pin per se. U.S. Pat. No. 4,620,342 includes fasteners at 16 which engage with the bearing plate 2. As best as can be determined, the European patent to the same Assignee does not include fasteners whatsoever. These designs incorporate the ability of bending plates over the free end of the swivel bearing cup by means of appropriate forming-over tools. None of the portions are machined from a solid bar stock.
German Patent Application No. 3,300,527 describes a caster support having a two-part construction with a double-bearing race. The base support provided at 1 includes mounting openings to secure to a frame. The center portion of the item includes a substantially hook shaped portion 4 and 5 for capturing therebetween the ball bearings 10 and 11 separated by the flange portion 8 provided near the end of the horn affixed to the wheel 9. Such a structure is manufactured by mass production techniques by stamping the various portions required. As best as can be determined, no other structures are utilized for fastening the two-part construction.
Another example of a simpler arrangement is found in Great Britain Patent Application No. 2,292,776 wherein a caster fork is attached to a wheel formed of two parts, a leg portion and a body portion. The two portions are clamped together by means of screws or bolts with the screws or bolts extending substantially in a horizontal direction. In this manner, the loading is not transmitted through the screws or bolts. Specifically, FIGS. 6 and 7 illustrate a double-race design. The caster is assembled once the two parts are formed from die cast metal in one embodiment. The assembly may be easily disassembled as well for maintenance purposes.
U.S. Pat. No. 3,606,503 describes a low profile caster assembly wherein the inner and outer rings of the assembly are completely formed and secured to their respective support members by, for example, welding, soldering or gluing. The rolling elements are inserted through an opening which opens into the annular space between the races provided. The rings may be machined and formed automatically and tempered. A plug element is provided, preferably formed from plastic material and snapped into position to cover the access opening through which the rolling elements are fed.
U.S. Pat. No. 5,097,565 also teaches a caster assembly as best seen in FIG. 3 which includes a plug 60 to allow feeding of the ball bearings into the compact package.
U.S. Pat. No. 5,479,677 teaches an improved caster design as best seen in FIG. 2 which includes a cap member, a ring member and a rotary member which cooperate to confine a plurality of steel balls which are protected from water penetration. The design includes four fasteners for fastening through the assembly and includes an inner and outer ball bearing set.
U.S. Pat. No. 5,199,131 describes a caster assembly made up of a stem and a ball bearing retainer formed from reinforced plastic with the components being ultrasonically welded to the stem and retainer combination unit. The material is preferably glass-filled nylon. This unit, of course, will not withstand great loading even though the design incorporates a double-ball race.
U.S. Pat. No. 3,733,648 describes a caster assembly made from sheet metal parts including a single row of ball bearings wherein the two rings forming the race are restrained by deformation, such as folding the material of the housing and the form respectively. Another example of a formed structure is found in European Patent Application No. 265,390 wherein a fixing late 12 is fastened with regard to a base. Two rings of ball bearings are provided with the first ring of bearings having a larger diameter than the second ring of all bearings. The portions provided as best seen in FIG. 2 interlock to trap the ball bearings therebetween and are fastened in the sense that the portion 26a, an extension of portion 26 is riveted in final position. This structure does not require a pin therefor to hold the structure together.
In reviewing the prior art therefore in total, most of the structures are formed from either casting or sheet metal forming techniques. Nowhere within the prior art is there found a simple caster design wherein the caster parts are manufactured from suitable materials capable of being formed to a predetermined resistance to wear and fatigue by any suitable method wherein said portions interfit to provide a much improved caster assembly containing bearings provided for carrying the load applied to the caster and separate bearings being provided for the swiveling of the caster separate from the load-carrying bearings, wherein the races for the bearings in one embodiment are disposed at ninety degrees to one another.
It is therefore an object of this invention to provide a simple heavy duty caster and a method of manufacturing thereof.
It is a further object of this invention to provide a caster assembly which will accept loads of up to 30 tons.
It is a yet further object of this invention to provide a caster assembly which is economical to manufacture.
It is yet a further object of the invention to provide a caster assembly manufactured from suitable materials resistant to wear and fatigue when formed.
Further and other objects of the invention will become apparent to those skilled in the art when considering the following summary of the invention and the more detailed description of the preferred embodiments illustrated herein.